Kohler and Milstein, in their seminal 1975 paper, said of hybridomas: "Such cultures could be valuable for medical and industrial use." Today, the use of monoclonal antibodies (mAbs) ranges from therapeutics to countless reagents, yet their mode of production remains largely unchanged, generally involving some form of in vitro or in vivo animal cell culture. While the cost of these molecules has decreased over time, they remain expensive to produce, whether it be as therapeutics or simple laboratory reagents. Currently, there are three principle means for the production of mAbs for use as reagents and diagnostics, including culture of hybridomas, re-introduction of hybridomas into mice and subsequent generation of ascites and transfection of mammalian cell lines with specific heavy and light chain antibody genes. Recently, we at Rincon Pharmaceuticals, Inc., have made considerable progress in the expression of recombinant proteins, including antibodies, in the chloroplast of the unicellular, eukaryotic, green alga, Chlamydomonas reinhardtii. The chloroplast of C. reinhardtii offers tremendous advantages over traditional mAb expression platforms when it comes to speed, scalability, COGs and capital costs to build a facility. In this proposal, we seek to express mAbs that will be used as immunoaffinity reagents. Our collaborator, NeoClone, Inc. of Madison, Wl, has developed an effective immunoaffinity platform employing the E. coli Beta' epitope as a peptide tag, allowing single step purification of recombinantly expressed molecules fused to this tag. Neoclone's efforts to commercialize this technology, however, have met with limited success, primarily owing to the high cost associated with the production of NT73 for use as the purification matrix. A successful outcome of this proposal would demonstrate the efficacy of mAbs produced in the C. reinhardtii chloroplast for use as reagents, and ultimately therapeutics. Using algae as an expression platform for mAbs, weather they be used as reagents or therapeutics holds great promise for reducing the costs of these valuable bio-molecules. [unreadable] [unreadable]